The present invention relates to auger shredding devices and, more particularly, to auger shredding devices utilizing a tapered screw in a side discharge grinding chamber.
In order to crush and shred large, rigid objects such as wooden pallets, crates, utility poles, railroad ties, 55-gallon oil drums of concrete and the like, it is necessary to utilize a heavy duty device which typically includes one or more rotating augers within a grinding chamber shaped to conform to the auger flight. An example of such device is disclosed in Koenig U.S. Pat. No. 4,253,615. That device includes a grinding chamber within which is rotatably mounted a single auger having a cylindrical shaft and a tapered flight. The front wall of the chamber includes a centrally-located discharge opening which is coaxial with the rotational axis of the auger and the top of the grinding chamber is open to receive material to be crushed and shredded.
In operation, material deposited into the grinding chamber is pulled downwardly by teeth projecting from the periphery or the auger night and is crushed and shredded by the interaction of the auger flight with the grinding chamber walls, as well as meshing action of the auger teeth with breaker bars mounted on the grinding chamber walls.
Since the auger flight is tapered and is supported on a cylindrical shaft, the volume defined by the auger flight and outer shaft surface--the pumping volume--decreases along the length of the auger to the discharge opening. Accordingly, material which is crushed and shredded is at the same time compressed as it progresses along the grinding chamber to the discharge opening.
A similar device is disclosed in Worthington U.S. Pat. No. 4,227,849. That device is a garbage compactor which is attachable to a garbage truck and includes a conical chamber which houses a powered auger having a cylindrical shaft and a tapered flight. The auger projects the length of the housing and extends outwardly beyond the discharge opening.
The top of the housing is open to receive residential refuse and the refuse is broken up and compressed as it is pumped by the rotating auger along the housing. With both the Worthington and Koenig devices, material is compressed by a tapered auger as it is pumped along the grinding chamber or housing to a discharge opening.
A disadvantage with these designs is that the compression of pumped material may, in some instances, cause jamming of the auger. In addition, a buildup of material at the front wall may result from the overcompression of material by the tapered flight, causing clogging of the discharge opening.
Another disadvantage of the aforementioned devices is that material often jams behind the first turn of the auger flight. The space beneath the first turn of the auger flight typically forms a wedge-shaped void with a disc-shaped auger mounting plate or rear wall of the grinding chamber which supports the auger shaft. When material is fed downwardly into the grinding chamber and is broken up, there is a tendency for material to enter that wedge-shaped void and build up. Accordingly, it is necessary to stop rotation of the auger and remove material from the space.
Another disadvantage with present designs is that torque transmitted from the auger motor to the auger flights must pass substantially entirely through the auger shaft, which places a strain on the weldments or other connections between the shaft and flight. With large diameter flights, a large shear stress is placed on the connection between the flight and shaft, resulting in failure of the weldment or connection in high torque operating situations. One solution to this problem is to increase the diameter of the shaft. However, such a solution is costly, greatly adds to the overall weight of the device, and reduces the volume of usable space within a grinding chamber of given dimensions.
Accordingly, there is a need for an auger shredder which provides an even and consistent flow of material along the grinding chamber to the discharge opening. There is also a need for an auger shredder in which the auger is capable of withstanding high torque loads with a minimum shaft diameter.